In principle, all implants inserted into the body can loosen. Almost ten percent of all endoprostheses loosen within the first ten years after implantation. The longer an implant is in the body, the more likely it is to become loose. Endoprostheses that are exposed to greater stress, such as hip joint endoprostheses (acetabular loosening) and knee joint endoprostheses , are particularly frequently affected. Loosening of these two endoprostheses is also of particular importance because their treatment is very costly.
Endoprostheses that are subject to heavy loads, such as hip joint endoprostheses, are particularly frequently affected.
Depending on the cause of the prosthesis loosening, two basic forms can be distinguished:
- Septic prosthesis loosening, which is due to an infection in the area of the implant - hence the term "septic" = involving (disease) pathogens. Bacterial colonization of the implant is one of the serious complications of joint replacement surgery.
- All endoprosthesis loosenings in which no pathogens are involved (= aseptic) are therefore classified as aseptic prosthesis loosenings.
The first symptoms of a loosened endoprosthesis are often pain in the area of the endoprosthesis during weight-bearing. As the loosening progresses, the pain can already occur at rest. However, bone fractures at or near the implantation site as well as malpositions and dislocations of the artificial joint can also be the result of a loosened endoprosthesis.
In the event of an acute bacterial infection of the implant, this can lead to
- Redness,
- swelling and
- warming
of the skin in the area of the implant with pain and impaired joint function. Patients often also develop chills and fever. Occasionally, the scar opens and pus leaks out.
Causes of septic prosthesis loosening
Even if surgeons take the greatest possible care during joint replacement surgery, in rare cases (in around one to two percent of patients) bacteria can be introduced to the implant. Normally, the body's defense system can destroy small amounts of bacteria. However, if there is a foreign body - such as the implant - in the body, the immune system's ability to defend itself in the area of the foreign body is weakened. The bacteria can then multiply more easily and form a kind of biofilm that fills the space between the bone and the implant. As a result, the implant cannot grow properly into the bone and it loosens.
Several factors have been identified that increase the risk of bacterial colonization and thus septic prosthesis loosening, such as
Alcohol and nicotine are risk factors for prosthesis loosening.
Causes of aseptic denture loosening
Abrasion-induced bone resorption is the most common cause. The sliding of the joint partners (sliding pairing) under high mechanical loads leads to increased abrasion of particles. This leads to wear and tear and, as a result, to loosening. According to one theory, the abrasion particles also induce an inflammatory reaction. As a result, bone is broken down and the prosthesis loosens.
Bone cement fractures, crack formation and material breakage are also held responsible for prosthesis loosening.
Furthermore, factors such as
- Primary stability when implanting the prosthesis,
- surgical experience and quality,
- surgical technique and
- the design and the material used for the implant
are also important as to whether and when the prosthesis loosens.
Patient-related risk factors for aseptic prosthesis loosening include, for example
- Advanced age
- weight
- Accident, fall
- Previously damaged bone(osteoporosis, bone necrosis)
- Pre-existing conditions (axial misalignment, diabetes, etc.)
Initial indications of prosthesis loosening include
- Type of complaints,
- other symptoms,
- Time of joint replacement surgery,
- previous illnesses and
- any traumatic events.
If a non-fixed prosthesis is suspected, an X-ray of the affected joint region is taken and, if possible, compared with the X-ray taken at the time of implantation.
If necessary, further imaging examinations, such as
- Sonography (ultrasound examination),
- MRI (magnetic resonance imaging),
- CT (computer tomography) or
- scintigraphy (examination using radioactively labeled substances)
are required to confirm the diagnosis or clarify specific questions.
If a septic cause is suspected, laboratory tests of the blood (e.g. determination of inflammation parameters) and an examination of the joint punctate, including the detection of bacteria, may be necessary.
Orthopaedic and trauma surgeons with extensive experience in arthroplasty arespecialists in prosthesis loosening.
If an endoprosthesis has become loose, the implant must first be removed (known as explantation). A new implant (known as a revision endoprosthesis) is then inserted. In the case of aseptic prosthesis loosening, explantation and re-implantation are usually performed as part of an operation. This procedure is also known as a one-stage replacement operation.
The treatment of septic prosthesis loosening is considerably more complex. In uncomplicated cases, which tends to be the exception, a one-stage replacement operation can also be performed. The implant and the infected tissue are removed in one session, the area around the implant is extensively cleaned and rinsed and a new prosthesis is inserted.
In most cases, however, a two-stage replacement operation is necessary. First, the loosened prosthesis and all materials and infected tissue are removed. Then, in certain joints (knee and upper ankle joint), material containing antibiotics is inserted over a period of several weeks. This treats the infection and stabilizes the bone. In addition, intravenous and oral antibiotics are also administered for several weeks. The new implant can only be inserted once the infection has been successfully treated.
In the case of aseptic prosthesis loosening, endoprosthesis replacement surgery is complex, but modern implants and materials usually make it possible without any problems.
The course and prognosis of septic prosthesis loosening are much more difficult to predict due to the infection process. The decisive factor is whether the infection has been completely brought under control and the revision endoprosthesis does not become infected again. It may be necessary to perform another replacement operation with the steps described above to treat the infection. Under certain circumstances, however, it may also be advisable to stiffen the joint. However, if the infection cannot be brought under control and continues to spread, it may be necessary to amputate a limb.
Prosthesis loosening can only be prevented to a limited extent, as most of the causes cannot be influenced by the patient. However, it is important that heavily overweight patients reduce their weight after the implantation of an artificial joint in order to reduce the load on the joint. You should also only engage in sports and activities that put a strain on the joint in consultation with your doctor. You should avoid excessive alcohol and nicotine consumption and abstain completely from drugs.